Since the discovery of the photosensitivity effect in germania fibers wherein he refractive index of an optical waveguide can be increased by exposing the waveguide to a light source, a variety of devices such as optical filters, WDMs, reflectors, and others, have been made and proposed. These devices often employ a long period grating (on the order of a few hundred microns) which couples light over a narrow band of wavelengths from the core layer of a waveguide to the cladding layer thereby acting as a wavelength selective loss element. An application for this type of device is, for example, the flattening of the gain spectrum of an erbium doped fiber amplifier. Various methods have been described for inducing periodic variations in the index of refraction in the core region of a photosensitive optical fiber, including the use of interferometric fringe patterns, phase masks, point by point index variation, and others. A discussion of the background, methods, and photoinduction process involved in making fiber gratings can be found in Hill et al., Photosensitivity in Optical Fibers, Annual Review of Materials Science, 23, 1993, 125-157. More recently, several articles by Vengsarkar et al. have been published which describe the theory and manufacture of long period fiber gratings and their use as band rejection filters, gain equalizers and sensors. In Vengsarkar et al., Long-period fiber gratings as band-rejection filters, in Proceedings of Conference on Optical Fiber Communications, OFC '95, post-deadline paper, PD4-2, 1995, and Bhatia et al., Optical Fiber Long Period Grating Sensors, Light News, Fiber and Electro Optics Research Center, Virginia Technical Institute and State University, pp. 6-11 (Winter 1995), both of which are herein incorporated by reference, a set-up is proposed for fabricating a long period grating in a hydrogen loaded (3.4 mole %) germanosilicate fiber exposed to 248 nm radiation from a KrF excimer laser through a chrome plated amplitude mask having a periodic rectangular transmittance function. The use of a chrome plated amplitude mask as suggested in these publications is limited to attempting to provide a fixed period grating designed for a particular loss wavelength. Further, the chrome on silica masks have a damage threshold of about 100 mJ/cm.sup.2 -pulse before the chrome is ablated, limiting the light source fluence used and the mask longevity.